1. Field of the Invention
The present invention relates to a method for breaking and cutting a glass ribbon and an apparatus therefor, in particular a method for breaking and cutting a glass ribbon and an apparatus therefor wherein fine glass fragments are not generated.
2. Discussion of the Background
In order to cut a glass plate, there has been used a method wherein a cutting wheel made from, e.g., cemented carbide, is pressed against a glass plate under a constant load to form a scratched line in the glass plate, and then the glass plate is bent along the scratched line to apply a bending moment to the glass plate so as to break and cut the glass plate.
In order to prevent the actual breaking and cutting line from deviating from a planned breaking and cutting line or to fail to break a glass plate as planned, it is necessary to apply a sufficiently great load when the cutting line is formed. As a result, a median crack which is essentially required for cutting and which progresses in the thickness direction of the glass plate, and lateral cracks which progress in substantially parallel to a surface of the glass plate are created in a crustal portion of the glass plate by the cutting line. Since these cracks exfoliate from the cutting line, or after breaking and cutting the glass plate, occurrence of fine glass fragments is unavoidable.
That fine glass fragments adhere to, e.g., a supporting table for the glass plate to form fine scratches on the glass surface. Fine glass fragments which have adhered to the glass surface sometimes scratch the glass surface in washing. Fine glass fragments which are not removed by washing sometimes scratch the surface of the glass plate when it is polished or when the glass plate is put on another glass plate.
As a breaking and cutting method wherein fine glass fragments are not liable to be generated, there has been known a method to cause thermal stress by a CO.sub.2 laser to break and cut a glass plate (F. P. Gagliano & R. M. Lumley, Proc. of the IEEE, vol. 57, no. 2, 1969). It has also been known to apply this method to break and cut a glass plate in a desired shape (JP-B-313040).
These known methods have a problem in that breaking and cutting stop a minute length from the edge of the glass plate, and do not reach an opposite end of the glass plate. If such a glass plate is broken or cut again, required dimensional accuracy can not obtained.
In FIG. 4, there is shown a perspective view of an actual breaking and cutting line which does not reach the opposite end. The starting point of the actual breaking and cutting line 22 is a preliminary break 21 which has been formed on an end of a glass plate 10. Reference numeral 23 designates a portion where the breaking and cutting line has not been formed.
In these methods, the preliminary break which acts as a starting point of breaking and cutting has to be formed in a portion adjacent to an end of a glass plate when the glass plate is broken and cut. Forming the preliminary break is likely to produce fine glass fragments.
There has not been known a method wherein a glass ribbon which has been formed according to, e.g., a floating process, is cut by thermal stress in an on-line situation.